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Abdominal Aortic Aneurysm

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Abdominal Aortic Aneurysm, Aortic Aneurysm of Abdominal Aorta, Abdominal Aortic Ectasia

  • Definitions
  1. Abdominal Aortic Aneurysm
    1. Abdominal aorta diameter 3.0 cm or greater
  2. Abdominal Aortic Ectasia
    1. Abdominal aorta diameter 2.5 to 2.9 cm
  • Epidemiology
  1. AAA Repair Incidence in U.S.: 45,000 surgeries per year (elective and emergent)
  2. Ruptured AAA results in 4500 to 11,000 deaths per year in the United States
    1. Responsible for 4-5% of sudden deaths in the United States
  3. Age Distribution
    1. Age under 50 years old
      1. Uncommon
    2. Age over 60 years
      1. Incidence 1.5% of men over age 60 years (1% of women over age 65 years)
      2. Accounts for 75% of aneurysms
    3. Age 65 to 74 years old
      1. Tenth leading cause of death
      2. Men: 10% Incidence of AAA (65 to 80 years old)
      3. Women 1% Incidence of AAA (65 to 80 years old)
    4. Ages 74-84 years old
      1. Men: 12.5% Incidence of AAA
      2. Women: 5.2% Incidence of AAA
  4. Male:Female Ratio
    1. Age: 60-64 year old: 11:1
    2. Age: 85-90 year old: 3:1
  5. Ethnicity
    1. Black and hispanic patients are at lower risk of AAA
  • Pathophysiology
  1. Elastin and Collagen degradation in aorta wall
    1. Inflammatory cells (T Cells, B Cells and Macrophages) release Matrix Metalloproteinase (proteolytic enzyme)
    2. Matrix Metalloproteinase degrades collagen Smooth Muscle and vessel elasticity
  2. Provoked by environmental stressors
    1. Inflammation (esp. Tobacco Abuse)
    2. Possible association with Chlamydia pneumoniae
    3. Increased wall tension (e.g. Hypertension, PVD)
  • Risk Factors
  • AAA Development
  1. Similar to other Cardiovascular Risk Factors
  2. Age over 65 years old
  3. Male gender
  4. Tobacco Abuse (75 to 90% of patients have used Tobacco)
  5. First degree relative has up to a 19% risk of AAA
  6. Coronary Artery Disease (including prior Myocardial Infarction)
  7. Peripheral Arterial Disease
  8. Hypertension
  • Risk Factors
  • AAA Rupture
  • Causes
  1. Associated with Atherosclerosis in only 25% of patients
  2. Aortic Dissection
  3. Mycotic Infection
  4. Cystic Medial Necrosis
  5. Ehlers-Danlos Syndrome
  • Presentation
  1. Asymptomatic in 75% of AAA
  2. Abrupt onset severe pain unrelieved by position change
    1. Classic: Back pain or Abdominal Pain, pulsatile mass and Hypotension
    2. Suggestive of aneurysm enlargement or rupture
    3. Classic triad only present in 25-50% of cases
  3. Cryptic presentations are common
    1. Misdiagnosis as Diverticulitis, GI Bleed, Musculoskeletal cause is common (60% initial misdiagnosis rate)
    2. May present as referred pain to a wide range of regions (to chest, back and Scrotum)
    3. Microscopic Hematuria (and rarely Gross Hematuria) may lead to misdiagnosis of Renal Colic
  4. Aortic Rupture (20% present ruptured)
    1. Free Intraperitoneal Rupture (Catastrophic)
      1. Acute abdominal or back pain
      2. Flank Ecchymosis
      3. Cardiovascular Collapse (Hypotension)
      4. Sudden Death
    2. Sentinal Bleed (small posterolateral wall tear)
      1. Acute pain (constant)
      2. Syncope
      3. Pulsatile abdominal mass
      4. Hemodynamically stable with Tachycardia
      5. Needs Emergent Intervention before full rupture
  • Symptoms
  1. Pain in Abdomen, Flank or Back
  2. Early satiety
  3. Nausea and Vomiting
  4. Hypotension
  5. Leg weakness
  • Signs
  • Pulsatile abdominal mass
  1. Technique
    1. Mass occurs left of midline at level of Umbilicus
    2. Position patient supine, knees flexed, while exhaling
    3. May be associated with abdominal bruit
  2. Efficacy of palpation for pulsatile mass >3 cm (decreased accuracy in Obesity)
    1. Test Sensitivity: 68%
    2. Test Specificity: 75%
    3. Fink (2000) Arch Intern Med 160(6):833-6 [PubMed]
  3. Larger AAA has higher likelihood of palpation
    1. AAA 3-4 cm palpable in 29% of cases
    2. AAA 5 cm palpable in 76% of cases
    3. Lederle (1999) JAMA 281:77-82 [PubMed]
  • Signs
  • Peripheral pulses
  1. Check pulse
    1. Femoral artery
    2. Popliteal artery
  2. Interpretation
    1. Bounding Pulse suggests possible AAA
    2. Loss of bilateral pulses may occur with AAA
    3. Peripheral artery aneurysmal swelling
      1. Femoral artery aneurysm predicts AAA in 85% of cases
      2. Popliteal artery aneurysm predicts AAA in 62% of cases
  • Signs
  • Miscellaneous
  1. Cullen's Sign
    1. Periumbilical Bruising
  2. Grey Turner's Sign
    1. Flank Bruising (retroperitoneal Hematoma)
  • Diagnosis
  1. AAA is most commonly identified as an Incidental Imaging Finding
  2. Normal abdominal aorta diameter
    1. Male: 17-21 mm (infrarenal)
    2. Female: 15-19 mm (infrarenal)
  3. Abnormal Localized aortic dilatation
    1. Aortic diameter exceeds 1.5 times normal size
    2. Aortic diameter exceeds 30 mm
  1. See Ultrasound in Abdominal Aortic Aneurysm
  2. See CT in Abdominal Aortic Aneurysm
  3. Incidental Findings on Abdominal XRay (low Specificity)
    1. Calcified AAA wall visible in only 67-75%
    2. Soft Tissue Mass
    3. Loss of psoas shadow
    4. Loss of renal outline
  • Imaging
  • Screening for Abdominal Aortic Aneurysm
  1. Background
    1. Primary care providers, with training, may perform bedside screening with good accuracy (consider in rural areas)
      1. Blois (2012) Can Fam Physician 58(3): e172-8 [PubMed]
  2. Indications for one-time routine screening
    1. USPTF Guidelines (2014, 2019)
      1. General screening above age 75 years is not typically recommended due to likelihood of comorbidity
      2. Men 65 to 75 years old
        1. Other AAA Risk Factor (see risk factors above, Level C recommendation)
        2. History of Tobacco Abuse (>100 Cigarettes lifetime, Level B recommendation)
          1. NNT: 294 to prevent aneurysm rupture
          2. NNT: 917 to prevent aneurysm rupture related mortality
      3. Women 65 to 75 years old
        1. History of Tobacco Abuse (inconclusive, consider screening)
      4. References
        1. Owens (2019) JAMA 322(22):221-18 [PubMed]
    2. Society for Vascular Medicine Guidelines
      1. Men age 60 to 85 years
      2. Women age 60 to 85 years with Cardiac Risk Factors
      3. Men and Women age >50 years and history of AAA in first degree relative
  3. First choice imaging study
    1. See Ultrasound in Abdominal Aortic Aneurysm
  4. Alternative for Obesity or excess intestinal gas
    1. Standard CT (see CT in Abdominal Aortic Aneurysm)
  • Imaging
  • Monitoring protocol for Abdominal Aortic Aneurysm
  1. Ultrasound in Abdominal Aortic Aneurysm
    1. Aorta diameter <3.0 cm
      1. No surveillance (although some consider rescreening if 2.5 to 2.9 cm)
    2. Aorta diameter 3.0 to 3.9 cm
      1. Repeat Ultrasound of AAA every 2 to 3 years
      2. Typical rate of expansion: 1-4 mm/year
    3. Aorta diameter 4.0 to 4.9 cm
      1. Repeat Ultrasound of AAA (or CT in Abdominal Aortic Aneurysm) every 12 months
      2. Typical rate of expansion: 3-5 mm/year
    4. Aorta diameter 5.0 to 5.4 cm
      1. Repeat Ultrasound of AAA (or CT in Abdominal Aortic Aneurysm) every 6 months
      2. Surgical Consultation for elective repair in women
      3. Consider Surgical Consultation in men (esp. for faster rate of expansion)
      4. Typical rate of expansion: 3-5 mm/year
    5. Aorta diameter >5.4 cm
      1. Surgical Consultation for elective AAA repair
      2. Typical rate of expansion: 7-8 mm/year (for AAA >6.0 cm)
  2. CT in Abdominal Aortic Aneurysm
    1. Indications
      1. Surgeon will order on referral
      2. See surgery indications below
      3. Ultrasound aorta >5.4 cm
      4. Change >0.5 cm in 6 months or >1 cm in 1 year
    2. Interpretation
      1. Repeat Ultrasound every 3 months if aorta <5.5 cm
      2. Vascular surgery consult for indications below
      3. Admit patients with aorta >8 cm on CT Abdomen
  • Imaging
  • Preoperative evaluation
  1. First Choice
    1. CT Angiogram
  2. Alternative in specific circumstances
    1. Abdominal Aortography
    2. MRI with MRA in abdominal aortic aneurysm
  • Precautions
  1. Delayed diagnosis of AAA related symptoms has a very high mortality
  2. Risk of AAA rupture when >6 cm: 10% per year
  3. Have a low threshold for bedside Abdominal Aorta Ultrasound in age >50-60 years with Abdominal Pain or back pain
  • Management
  • Preoperative Risk Reduction
  1. See Preoperative Cardiovascular Evaluation
  2. Aspirin or Plavix
    1. AAA is a significant Cardiovascular Risk Factor
  3. Perioperative Beta Blocker
    1. Significantly decreases mortality
    2. Used Bisoprolol 5 mg daily >1 week pre-surgery
    3. Goal Heart Rate: 60 (keep systolic BP >100)
    4. Poldermans (1999) N Engl J Med 341:1789-94 [PubMed]
  4. Tobacco Cessation
  5. Statins for lipid lowering
  6. COPD optimization
  7. Renal Function optimization in Chronic Kidney Disease
  8. Avoid competitive sports and intense Isometric Exercise
  • Management
  • Surgical Repair
  1. Indications: Symptomatic Aneurysm
    1. Symptoms: Abdominal, back or Groin Pain with AAA
      1. Concurrent Hypotension suggests ruptured AAA
    2. Urgent surgical repair (high risk of rupture)
  2. Indications: Asymptomatic Aneurysm
    1. Aortic aneurysm diameter >5.4 cm
    2. AAA diameter 4-5 cm and
      1. Enlarging 0.5 cm in 6 months or
      2. Enlarging 1 cm in 1 year
    3. AAA diameter 7 cm with significant comorbidity
      1. Left Ventricular Dysfunction (CHF)
      2. Severe Chronic Obstructive Pulmonary Disease
      3. Noncorrectable symptomatic Coronary Artery Disease
  3. Operative Risk
    1. Myocardial Infarction (4.7% mortality)
    2. Mortality
      1. Elective repair: 3-5% (similar risk )
      2. Symptomatic Aneurysm: 26%
      3. Ruptured Aneurysm: 35-40%
      4. Sullivan (1990) J Vasc Surg 11:799-803 [PubMed]
  4. Operative techniques
    1. Open AAA repair (traditional)
      1. Background (infrarenal technique)
        1. Aorta is cross clamped above and below the aneurysm
        2. Graft is sewn into the defect and the vessel is closed over the graft
      2. Higher 30 day mortality (4-5%) than endovascular repair (1-2%)
        1. However, endovascular repair benefit is absent by 1-2 years following repair
        2. Greenhalgh (2010) N Engl J Med 362(20): 1863-71 [PubMed]
      3. Endovascular repair has a higher rate of later complications than open repair
        1. Graft complications
        2. Second procedures required
      4. Survival after first 30 days following open repair
        1. Five year survival: 64%
        2. Ten year survival: 33%
    2. Endovascular AAA repair (Endograft, EVAR)
      1. Background (infrarenal technique)
        1. Endovascular graft is inserted via a small incision in the femoral artery
      2. Accounts for 80% of intact AAA repairs and 52% of ruptured AAA repairs
        1. Guirguis (2019) JAMA 322(22): 2219-38 [PubMed]
      3. Optimal emergency stabilization procedure if infrarenal AAA (especially in elderly patients)
      4. Also consider if high risk with <2 years Life Expectancy
      5. Surveillance post procedure (for graft migration, endoleaks, AAA expansion)
        1. Requires CT at 1, 6 and 12 months after procedure
        2. Annual surveillance required after the first year
      6. Adverse events (10-15%)
        1. Lower 30 day mortality than open AAA repair
        2. Risk of blood leakage around endograft
        3. Also risk of stent or graft migration
        4. Similar 5 year mortality outcomes to open repair
      7. References
        1. (2005) Lancet 365:2179-86 [PubMed]
  • Prognosis
  1. Mortality from ruptured aneurysm: 80-90% (50% do not reach the hospital alive)
  2. Elective AAA Repair: 61% five year survival
  3. Risk of AAA rupture
    1. AAA <5.5 cm: 0.6-3.2% annual risk of AAA rupture
    2. AAA 5.5 - 6 cm: 9% annual risk of AAA rupture
    3. AAA 6 - 6.9 cm: 10% annual risk of AAA rupture (40% lifetime risk of rupture)
    4. AAA 7 cm: 33% annual risk of AAA rupture (50% lifetime risk of rupture)
  4. Course of small aortic aneurysms (<4 cm)
    1. Increase median of 2 mm per year (up to 8 mm/year)
    2. Biancari (2002) Am J Surg 183:53-5 [PubMed]
  5. Comorbid cardiopulmonary disease is common in AAA
  • Prevention
  1. Slowing progression of AAA
    1. Tobacco Cessation
      1. Tobacco increases the incremental AAA growth rate by 0.4 mm per year
      2. Sweeting (2012) Br J Surg 99(5): 655-65 [PubMed]
    2. No strong evidence for specific antihypertensives or lipid lowering agents prior to repair
  2. Patient Education
    1. Indication for immediate evaluation in known AAA
    2. Pain in low back, groin, legs or buttocks